I think it's a common enough occurrence that when we re-read something we find new stuff in a text. We either notice stuff we missed the first time around or we can connect it to new thoughts in our head. That's why I reread the 1st edition DMG from cover-to-cover every couple of years (Though it's been more like three right now. That's grad school for you, I guess.). And there's a line from an Frantz Fanon piece that I didn't understand when I was assigned it as an undergrad and I didn't understand it when I was assigned it again the first year of my Masters degree. Just last spring I was assigned the same chapter a third time and I think I've finally got the gist of that one sentence now, but I don't understand it well enough to trot it out casually in a discussion, or to make it a key component of a paper. Maybe that'll come later, after further wrestling with the piece some more.
Which brings me to an idea I've been pondering for a while now: levels of spell comprehension. Because the world needs one more way to make M-U's more complicated, right?